Refrigeration compressors have been object of studies that aim at improving the performance of these compressors. Among the various points of this performance to be improved, one can point out the increase of the amount of refrigerant gas drawn during suction and the reduction of the power required to compress the refrigerant gas. In order to achieve such objectives, it is necessary to reduce the temperature of the refrigerant gas in the suction (increasing its specific mass) and also to reduce the temperature of the compression chamber wall which contacts the refrigerant gas. The development of solutions which promote the reduction of the temperature levels of the compressor and of the flows dissipated by the hot parts thereof is one of the feasible ways to reach these goals.
Hermetic compressors of the type used in refrigeration systems usually comprise, in the interior of a housing, a motor-compressor assembly having a cylinder block in which is defined a cylinder having an end closed by a head and internally defining a discharge chamber in selective fluid communication with a compression chamber defined inside the cylinder and closed by a valve plate provided between the cylinder closed end and the head, said fluid communication being defined through suction and discharge orifices provided in the valve plate and which are selectively and respectively closed by suction and discharge valves, which are usually carried by the valve plate. One of the major causes responsible for heating the internal components of the compressor is its discharge system, which comprises the entire path of the refrigerant gas, from its exhaustion from the compression chamber to the discharge of said refrigerant gas from the inside the compressor. This is because the refrigerant gas reaches the highest temperature levels during its compression inside the cylinder of the motor-compressor assembly, and the heat generated by said compression is dissipated for the other components of the compressor, during the path of the refrigerant gas from the compression chamber inside the cylinder to its discharge from the inside the compressor housing.
One solution to avoid this energy dissipation is to insulate the gas discharge system from the rest of the compressor. By doing this, the extremely hot gas exhausted from the compression chamber will pass through the discharge system without transferring heat to the other components, thereby reducing the temperature levels of the compressor as a whole. Solutions to insulate the discharge system may be found in U.S. Pat. No. 3,926,009, in which the gas discharge tube is defined having a double wall, in order to minimize heat transfer of the gas under compression to the interior of the housing, and in U.S. Pat. No. 4,371,319, in which each of the parts of cylinder cover, discharge muffler and discharge tube is surrounded by a thermal insulating element with the same purpose of minimizing heat transfer of the gas under compression to the interior of the housing disclosed in U.S. Pat. No. 3,926,009. In the vast majority of the refrigeration hermetic compressors, mainly of the reciprocating type, the compressor discharge system comprises a first discharge chamber defined inside the cylinder cover, and located after the valve plate and which receives the gas coming from the compression cylinder. This gas passes subsequently through other chambers before reaching a compressor discharge tube, which leads the compressed refrigerant gas out from the compressor housing to a refrigeration system to which said compressor is usually associated.
Studies have proved that one of the major causes responsible for heating the compression cylinder is the heat flow generated by the gas in the cylinder cover, which heats the valve plate and, by conduction, heats the top of the cylinder block, in the region of the compression chamber of the compression cylinder. The reduction of this heat flow has a positive impact in reducing the temperature of the cylinder and consequently in reducing the compression power.
The known prior art presents different alternatives to make possible a reduction of the heat transfer from the cylinder cover region to regions inside the housing distant therefrom. There are known devices, such as heat exchangers, for example “Stirling” machines, as taught in U.S. Pat. No. 6,347,523; the provision of fins on the heads and the use of an auxiliary air motion system; the use of heat pipes; the use of fluid pumping system using pumps driven by mechanic or electric oscillating motion, among others. However, said known solutions do not minimize the heat transfer between the cylinder cover and the cylinder block, due to the gas discharge from the compression chamber to the discharge chamber.